If you’ve been mulling over whether or not it’s time to buy or replace a dishwasher, here’s the information that could put you over the edge: There are 54 billion bacterial cells on a single cubic centimeter of the average kitchen sponge. They are breeding grounds for all types of germs and bacteria. Dishwashers are naturally a much more sanitary way to wash and disinfect dishes, utensils, glasses, and some cookware (but don’t you dare put your cast iron in there).
You might already know that it’s your kitchen, not your bathroom, that has the most microbial activity, and that’s indeed because of your sponge—”the biggest reservoirs of active bacteria in the whole house.” But did you know that cleaning your sponge only makes things worse? Sticking your sponge in the dishwasher or boiling water to disinfect is a no-go, and leaving it to sit in soapy water at the bottom of your sink is also a bad idea. Yes, really.
In a 2017 study published in the journal Scientific Reports, researchers in Germany found that used kitchen sponges were home to dozens of bacterial microorganisms (the researchers charted just the top 20 bacteria), and out of the top 10 most abundant bacteria, five were closely related to those classified as RG2, microbes associated with preventable human illnesses including food poisoning. The testing size was relatively small (14 sponges, separated by top and bottom into 28 samples), but the 10 most common bacteria were “quite ubiquitous,” the study notes.
What’s more, the samples taken from homes where they had been “regularly cleaned,” according to their owners, were even worse. In those sponges, two of the 10 most common RG2 bacteria, Chryseobacterium hominis and Moraxella osloensis, were found in “significantly greater proportions.”
“From a long-term perspective,” the researchers wrote, “sponge sanitation methods appear not sufficient to effectively reduce the bacterial load in kitchen sponges and might even increase the shares of RG2-related bacteria.”
And because kitchen sponges typically get used for multiple tasks (not just cleaning dishes, but wiping countertops and scrubbing any number of sticky surfaces), our sponges aren’t just a “reservoir of microorganisms,” the team writes, “but also as disseminators over domestic surfaces, which can lead to cross–contamination of hands and food, which is considered a main cause of foodborne disease outbreaks.” In other words, your sponge is really good at spreading bacteria all over your kitchen.
So what’s a conscientious (and now completely grossed-out) household to do? Well, you’ll be happy, and not that surprised, to learn that “notably, no bacteria could be detected in a collection of newly bought, i.e. unused kitchen sponges.” Since it’s run-of-the-mill kitchen activities that bring these bacterial colonies to life, the researchers suggest that we replace our sponges weekly. That’s right: ditch your sponges every single week. If you’re unsure whether it’s a good time to get rid of your sponge, give it a sniff. If it smells off or downright wretched, obviously toss it.
Though the team notes that more work needs to be done to measure the actual pathogenicity of the used kitchen sponge—that is, how are these sponges actually making us sick?— I feel comfortable saying that we should all just start fresh with a new sponge today, and start buying them in bulk.
Our Favorite Eco-Friendly Sponges
To eliminate so much waste, choose plant-based sponges that are entirely biodegradable to reduce waste and one’s carbon footprint. Our own Five Two Compostable Sponge Cleaning Cloths are an all-natural swap for paper towels or sponges, perfect for cleaning up countertop messes. They’re made from plant fibers and water-based ink, and are guaranteed to decompose in a home compost within six weeks.
Grove Collaborative also sells some of our favorite sponges made from plant-based, recycled materials: walnut shells, plant cellulose, and recycled PET (a type of plastic). If you’re shopping at a regular grocery store, keep an eye out for Scotch Brite Greener Clean Non-Scratch Scrub Sponges, which are made from natural plant fibers. With so many eco-friendly options, you can replace your sponge each week guilt-free.
If you want to get a much closer look at what’s living in your kitchen sponge, read the full study here.
This article was updated in March 2022 with even more cleaning recommendations from our editors.